The Transposon Registry

Tn6644 is a 5.1-kb composite transposon composed by two ISEnfa5 arranged in the same orientation flanking the cfr multiresistance gene. This structure has been found in several microbial species, either located in the chromosome or on plasmids. Its mobilization by transposition could be suggested observing the different target site duplications of 3 bp found in distinct genetic environments. A part of Tn6644 comprising a copy of ISEnfa5, the cfr gene and the sequences between cfr and two ISEnfa5 elements, is able to looping-out giving circular intermediates. The passenger gene cfr is a rRNA methyltransferase that acts on a conserved 23S rRNA residue, conferring resistance to an array of ribosomal antibiotics, including phenicols, lincosamides, pleuromutilins, streptogramins A, 16-member ring macrolides and oxazolidinones.

Tn6648 is a 53.2-kb composite element, found in Enterococcus faecalis strain Ef1. It composes of Tn5801.B15 (∼20.3 kb containing tetM resistance gene) and Tn6647 (∼32.8 kb)